Catalyst heating control method of parallel type hybrid vehicle

ABSTRACT

Disclosed herein is a catalyst heating control method for a parallel hybrid vehicle that can generate a predetermined torque required to maintain a stable no-load operation state of an engine when a catalyst is warmed in a cold-start state of the engine while sufficiently reducing the ignition efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application Serial Number 10-2006-0090067 filed on Sep. 18, 2006 with Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to control strategies for engines, and more particularly, to control strategies for rapidly heating a catalytic converter in a parallel type hybrid vehicle.

BACKGROUND OF THE INVENTION

A large amount of harmful substances is present in emissions at an initial startup stage of a vehicle engine. Emission control devices, such as catalytic converters, can reduce emissions generated by engine combustion. However, the effectiveness of such emission control devices varies with operating temperature. For example, the efficiency of an emission control device may be much greater at higher temperatures than it is at lower temperature. Thus, to enhance the efficiency of emission control device, it is important to rapidly heat a catalytic converter after starting of a vehicle to a certain point so that normal purification can begin in a short time. Typically, a “light-off” temperature has been used to signify a certain temperature above which a prescribed efficiency is achieved.

Various approaches have been made to rapidly heat catalytic converters after starting of a vehicle. One line of the approaches is to heat a catalyst by adjusting the temperature of discharge gas in the combustion process of an engine. One of the representative examples of such approach is the lean burn control method. In the method, an artificial ignition delay is introduced while a lean air-fuel ratio is maintained. By delaying ignition timing, discharge gas with higher temperature is supplied to a catalytic converter.

That is, the retardation of ignition timing, while reducing the ignition efficiency of an engine, provides additional heat to increase the temperature of discharge gas when a discharge port is opened instead of reducing the engine torque. The discharge gas with increased temperature directly heats the catalyst.

However, conventional systems utilizing the lean burn control method is difficult to rapidly heat catalytic converters when the ignition efficiency is required to be reduced to a range where the torque must maintain a stable no-load operation state of the engine.

There is thus a need for an improved catalyst heating control method that can generate a predetermined torque required to maintain a stable no-load operation state of an engine when a catalyst is warmed in a cold-start state of the engine while sufficiently reducing the ignition efficiency of the engine so that the catalyst can be warmed more rapidly.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.

SUMMARY OF THE INVENTION

The present invention provides catalyst heating control methods of a parallel hybrid vehicle that can overcome the problems associated with such conventional systems. The catalyst heating control methods according to the present invention allow a predetermined torque required to maintain a stable no-load operation state of an engine to be generated when a catalyst is warmed in a cold-start state of the engine while reducing the ignition efficiency of the engine enough to more rapidly warm the catalyst, thereby more efficiently purifying a large amount of harmful substances contained in discharge gas at an initial startup stage of the engine.

In one aspect, the present invention provides a catalyst heating control method for a parallel hybrid vehicle, comprising the step of compensating a reduced ignition efficiency of the engine with a motor torque.

In a preferred embodiment, the present control method comprise the steps of: (a) determining a target catalyst heating ignition efficiency; (b) calculating a catalyst heating engine torque; (c) calculating a no-load operation requirement torque of the engine to maintain a stable no-load operation state of the engine; (d) determining a motor compensation requirement torque; and (e) controlling a motor using the motor compensation requirement torque to maintain the stable no-load operation state of the engine by supplementing the torque of the engine operated with the target catalyst heating ignition efficiency.

Preferably, the target heating ignition efficiency may be set to have a reduced value in proportion to the maximum ignition efficiency where the maximum torque is exhibited. For example, the target heating ignition efficiency may suitably be determined by both an rpm of the engine and a charging efficiency after the engine is started. In a preferred embodiment, the target heating ignition efficiency may be determined by using a control map having the engine rpm and the charging efficiency as independent variables and the target catalyst heating ignition efficiency as a dependent variable. Suitably, the target catalyst heating ignition efficiency may be determined to be within a range from 50% to 70% of the maximum ignition efficiency.

Also preferably, the catalyst heating engine torque may be determined by both the target catalyst heating ignition efficiency and a charging efficiency of the engine at a given time. For instance, the catalyst heating engine torque may preferably be determined by using a control map having the target catalyst heating ignition efficiency and the charging efficiency as independent variables and a catalyst heating engine torque as dependent variable.

Furthermore, the engine no-load operation requirement torque may preferably be determined by both a basic ignition efficiency, which is required to maintain the normal no-load operation state of the engine, and a torque of the engine, which is output when operated with the charging efficiency at a given time. For example, the engine no-load operation requirement torque may be determined by using a control map having basic ignition efficiency values and charging efficiency values as independent values and engine no-load operation requirement torque values as dependent values.

In another preferred embodiment, the present catalyst heating control method may further comprise the step of determining whether the catalyst heating control is necessary. Preferably, the determination may be conducted by using the temperature of cooling water of the engine before the target catalyst heating ignition efficiency is determined and just after the engine is started.

In still another preferred embodiment, after the above step, an engine no-load operation control is started.

A preferred catalyst heating control method of the present invention may further comprise the steps of: (a) calculating an engine rpm difference, which is a difference between a current rpm of the engine and a normal rpm of the engine under no load; and (b) accumulating an elapsed time after the engine has been started.

Preferably, when the engine rpm difference is a predetermined value or less or when the accumulated elapsed time is a predetermined time or longer, the engine no-load operation control is stopped and the step of determining the target catalyst heating ignition efficiency is conducted. For example, the predetermined rpm difference may be 50 rpm and the predetermined elapsed time may be 7 seconds.

In another aspect, motor vehicles are provided that use a described catalyst heating control method.

It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like. The present catalyst heating control method will be particularly useful with a wide variety of motor vehicles.

Other aspects of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of the present invention, reference should be made to the following detailed description with the accompanying drawings, in which:

FIG. 1 is a flow chart illustrating a catalyst heating control method according to an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiment of the present invention. The embodiments are described below so as to explain the present invention by referring to the attached drawing.

Referring to FIG. 1, in a preferred embodiment of the present invention, after an engine is started, whether a catalyst heating control is required is determined. This determination depends on the temperature of cooling water of the engine just after the engine is started. The result of the determination in turn determines whether the catalyst heating control operation is conducted or not.

The reason for this is that the catalyst heating control is unnecessary in case where the engine is not cold-started but was running a short time ago.

After the catalyst heating control determination step, a typical no-load operation control of the engine is conducted.

That is, it is preferable that because the catalyst heating control determination step must be conducted as rapidly as possible in order to warm the catalyst in a short time when the engine is started, the catalyst heating control determination step is conducted before the engine no-load operation control, which maintains the no-load operation state after the engine has started, is conducted.

Of course, the engine no-load operation control must be conducted even when it is determined that the catalyst heating control is unnecessary at the catalyst heating control determination step.

Next, the step of calculating the engine rpm difference ΔN, which is a difference between the current rpm of the engine and the typical no-load rpm of the engine, and the step of accumulating the elapsed time after the engine has started, are conducted. When the engine rpm difference ΔN is a predetermined value or less or when the accumulated elapsed time is a predetermined time or longer, the engine no-load operation control is stopped and the step of determining the target catalyst heating ignition efficiency is conducted.

This functions to conduct a catalyst heating control after the engine has been started and the rpm of the engine has been stabilized. For example, in case where the current rpm of the engine is stabilized such that the difference between the current rpm of the engine and the rpm of engine under no load, which is a control goal in a normal state, is within a range less than 50 rpm, or when at least 7 seconds has elapsed after the engine has started, the catalyst heating control is conducted.

The target catalyst heating ignition efficiency is set to have a reduced value in proportion to the maximum ignition efficiency at which the maximum torque is exhibited in an engine state determined both by the rpm of the engine and by the charging efficiency.

Preferably, the target catalyst heating ignition efficiency is determined within a range from 50% to 70% relative to the maximum ignition efficiency determined by the rpm of the engine and the charging efficiency.

Typically, in case where the catalyst heating operation is not considered, the ignition efficiency is approximately 80% of the maximum ignition efficiency depending on the rpm of the engine and the charging efficiency, and is in a range within which knocking is prevented and it is possible to respond to disturbances, such as the operation of air conditioning. In the present invention, to rapidly heat the catalyst, the target catalyst heating ignition efficiency is set to a relatively low level, as described above. A motor, which will be explained below, compensates for the resulting shortage of engine torque.

In step of determining the target catalyst heating ignition efficiency, a control map can be used. Particularly, such a map may have values of the engine rpm and charging efficiency as independent variables and target catalyst heating ignition efficiency as a dependent variable, which is previously stored in the controller. A target catalyst heating ignition efficiency is selected from the map.

Next, the step of determining the catalyst heating engine torque, which is the torque generated by the engine depending on the determined target catalyst heating ignition efficiency and the present charging efficiency of the engine, is conducted.

In the step, a three-D control map can be used. Such a map may be obtained through experiments. It may have target catalyst heating ignition efficiency values and charging efficiency values as independent variables and catalyst heating engine torque values as dependent variables, which is previously stored in the controller. The controller selects a catalyst heating engine torque value from the three-D map depending on a target catalyst heating ignition efficiency value and a present charging efficiency value at a given time.

The catalyst heating engine torque, which is obtained through the above process, is a torque generated in the engine when the engine is operated in a state in which the temperature of discharge gas is relatively increased when a discharge port is opened, by artificially reducing the ignition efficiency of the engine to the target catalyst heating ignition efficiency. As a result, this torque value is less than that in the normal no-load operation state.

Thereafter, the step of calculating an engine no-load operation requirement torque to maintain a stable no-load operation state is conducted. The engine no-load operation requirement torque can be defined as a normal torque generated by the engine, which is operated under no load, when the catalyst heating control is not conducted.

In this step of calculating an engine no-load operation requirement torque, a basic ignition efficiency, which is required to maintain the normal no-load operation state of the engine, and the torque of the engine, which is output when operated with the charging efficiency at that time, are calculated. In the same manner, a control map may be obtained through experimentation. Particularly, such a map may have basic ignition efficiency values and charging efficiency values as independent values and engine no-load operation requirement torque values as dependent values, which is stored in the controller. An engine no-load operation requirement torque can be selected from the map.

Subsequently, the step of determining a motor compensation requirement torque by obtaining the difference between the engine no-load operation requirement torque and the catalyst heating engine torque is conducted.

In this step, a motor compensation requirement torque, which is required in order to maintain the stable no-load operation state of the engine despite the performance of the catalyst heating control, is calculated by subtracting the catalyst heating engine torque, which is generated by the engine when the catalyst heating control is conducted, from the engine no-load operation requirement torque, which maintains the stable no-load operation state of the engine when the catalyst heating control is not conducted.

Therefore, while the engine is operated in the state in which the target catalyst heating ignition efficiency is obtained by reducing the ignition efficiency to a state that can permit exhibition of the catalyst heating engine torque, the motor is controlled such that the calculated motor compensation requirement torque is obtained, thus complementing the torque of the engine operated with the target catalyst heating ignition efficiency. Then, the stable operation of the engine under no load is ensured, and, in addition, the catalyst can be rapidly warmed by the increased temperature of discharge gas due to the artificial reduction of ignition efficiency.

In other words, when the motor generates the motor compensation requirement torque, although the torque generated in the engine due to the reduced ignition efficiency is low compared to a typical engine, the catalyst can be rapidly warmed by a sufficiently high temperature of discharge gas, and simultaneously, the stable no-load operation state of the engine can be maintained by the motor compensation requirement torque.

In order to control the motor to obtain the motor compensation requirement torque, various control methods known to those skilled in the art can be used. For example, a proportion-integral control can be used.

As is apparent from the foregoing, catalyst heating control methods of a parallel hybrid vehicle according to the present invention overcomes the drawback of conventional systems. Specifically, the present method can generate a predetermined torque required to maintain the stable no-load operation state of an engine when a catalyst is warmed in a cold-start state of the engine while sufficiently reducing the ignition efficiency of the engine so that the catalyst can be warmed more rapidly. As a result, it ensures more stable idling state of the engine and more efficient purification of a large amount of harmful substances of discharge gas generated in an initial startup stage of the engine.

The invention has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents. 

1. A catalyst heating control method for a parallel hybrid vehicle, comprising the step of compensating a reduced ignition efficiency of the engine with a motor torque.
 2. A catalyst heating control method for a parallel hybrid vehicle, comprising the steps of: determining a target catalyst heating ignition efficiency; calculating a catalyst heating engine torque; calculating a no-load operation requirement torque of the engine to maintain a stable no-load operation state of the engine; determining a motor compensation requirement torque; and controlling a motor using the motor compensation requirement torque to maintain the stable no-load operation state of the engine by supplementing the torque of the engine operated with the target catalyst heating ignition efficiency.
 3. The catalyst heating control method as defined in claim 2, wherein the target heating ignition efficiency is set to have a reduced value in proportion to the maximum ignition efficiency where the maximum torque is exhibited.
 4. The catalyst heating control method as defined in claim 2, wherein the target heating ignition efficiency is determined by both an rpm of the engine and a charging efficiency after the engine is started.
 5. The catalyst heating control method as defined in claim 4, wherein the target heating ignition efficiency is determined by using a control map having the engine rpm and the charging efficiency as independent variables and the target catalyst heating ignition efficiency as a dependent variable.
 6. The catalyst heating control method as defined in claim 3, wherein the target catalyst heating ignition efficiency is determined to be within a range from 50% to 70% of the maximum ignition efficiency.
 7. The catalyst heating control method as defined in claim 2, wherein the catalyst heating engine torque is determined by both the target catalyst heating ignition efficiency and a charging efficiency of the engine at a given time.
 8. The catalyst heating control method as defined in claim 7, wherein the catalyst heating engine torque is determined by using a control map having the target catalyst heating ignition efficiency and the charging efficiency as independent variables and a catalyst heating engine torque as dependent variable.
 9. The catalyst heating control method as defined in claim 2, wherein the engine no-load operation requirement torque is determined by both a basic ignition efficiency, which is required to maintain the normal no-load operation state of the engine and a torque of the engine, which is output when operated with the charging efficiency at a given time.
 10. The catalyst heating control method as defined in claim 9, wherein the engine no-load operation requirement torque is determined by using a control map having basic ignition efficiency values and charging efficiency values as independent values and engine no-load operation requirement torque values as dependent values.
 11. The catalyst heating control method as defined in claim 2, further comprising the step of: determining whether the catalyst heating control is necessary using the temperature of cooling water of the engine before the target catalyst heating ignition efficiency is determined and just after the engine is started.
 12. The catalyst heating control method as defined in claim 11, wherein an engine no-load operation control is started after the step of claim
 11. 13. The catalyst heating control method as defined in claim 12, further comprising the steps of: calculating an engine rpm difference, which is a difference between a current rpm of the engine and a normal rpm of the engine under no load; and accumulating an elapsed time after the engine has been started.
 14. The catalyst heating control method as defined in claim 13, wherein when the engine rpm difference is a predetermined value or less or when the accumulated elapsed time is a predetermined time or longer, the engine no-load operation control is stopped and the step of determining the target catalyst heating ignition efficiency is conducted.
 15. The catalyst heating control method as defined in claim 14, wherein the predetermined rpm difference is 50 rpm and the predetermined elapsed time is 7 seconds.
 16. A vehicle using the catalyst heating control method of claim
 1. 17. A vehicle using the catalyst heating control method of claim
 2. 